The present invention relates to a filter cartridge which is suitable for filtering liquid and gas. More particularly, the present invention relates to a filter cartridge for filtering a liquid agent containing large amounts of various foreign matters, such as an amine-type organic release agent used on a substrate for electronic parts (e.g. a semiconductor wafer and a glass substrate for a liquid crystal device); a pigment-dispersion photoresist for a glass substrate of a liquid crystal device; a slurry for a chemical and mechanical abrasion device; and other liquids used in general industry.
Two different and specific basic cartridges generally used for filtering gas and liquid are a depth filter (representatively a roll type filter) and a membrane filter (usually a pleated filter). Today, roll type depth filters and membrane filters each encased in a separate housing are used in tandem to attain a desired purification level. In Japanese Patent Application Kokai No. 7-213814, a filter cartridge is proposed that has a filter body comprising: a depth filter containing non-woven fiber mass in the form of either roll or seamless fiber cylinder; and a pleated screen filter or a surface filter that can be encased in the same housing with the depth filter. However, there are still demands for combinations of filters that can attain specific properties, such as increasing throughput and removing metal ions. By separately providing filters each as a unit that can be combined to each other, production cost can also be reduced.
FIGS. 1 and 2 show a conventional filter cartridge disclosed in Japanese Patent Application Kokai No. 7-213814. A cartridge 10 has a depth filter 16 having an exposed outer surface 12, in the form of roll or seamless fiber cylinder; a pleated surface filter or screen filter 18 concentrically arranged in within the depth filter; a core 20 supporting the inner surface of the surface filter 18 as well as having a number of holes 23 as fluid passages; and a fluid outlet 14 for withdrawing a filtrate fluid (liquid or gas) from the core 20. The top end of the depth filter 16 and that of the surface filter 18 are sealed. The top end of the filter cartridge 10 is completely sealed with a cap 19. Upon its use, the filter cartridge 10 is inserted into a housing 21 of a filter device, and liquid-tightly fixed to the wall of the housing via a thread means and/or an O-ring provided around the fluid outlet 14.
A fluid (liquid or gas) to be purified is introduced between the housing 21 and the cartridge 10, and the fluid passes from the outer surface 12 towards the inside of the depth filter 16, and then through the surface filter 18. The purified fluid flows out to the central passage through the holes 23 of the core 20, and is withdrawn as a filtrate from the fluid outlet 14.
In the above-mentioned case in which two different filters are used, the filter located upstream has relatively large pore diameter, while the filter located downstream has relatively small pore diameter, in order to increase the level of purification and to elongate the life of the filter.
However, the above-mentioned two filters are integrally formed to be a single filter element, and have disadvantages in that various possible filter combinations should be prepared that satisfy various purposes. In addition, the upstream filter is contaminated faster as compared with the downstream filter, and thus even when the downstream filter is not contaminated, the filter element cannot be used anymore, because of the shorter life of the upstream filter.
Therefore, the object of the present invention is to provide a filter cartridge comprising an upstream filter unit and a downstream filter unit, wherein both units can be combined to each other so that the upstream filter locates between the downstream filter and the housing to form a cartridge and the combination can be properly selected depending on the purpose such as the removal of metal ions and can elongate the filter life.
The present invention provides a filter element comprising a combination of an upstream filter and a downstream filter, wherein the upstream filter is replaceable. As the result, the life of the downstream filter is elongated while attaining the required purified level, and in addition, smaller number of filters is required in order to obtain the same amount of filtrate as that in the case of the conventional filter.
The present invention also provides a filter element comprising an upstream filter and a downstream filter, each of which is properly selected depending on the specific purposes, from the stock of various filters expected to be used in various applications. The upstream filter should be replaceable, although it may be integrally formed as a part of a disposable filter device, if necessary.
Specifically stated, the preset invention provides a filter element comprising an upstream filter and a downstream filter, wherein said downstream filter has a means for fixing to a housing, and said upstream filter is fixable to said downstream filter fixed to said housing; and a filter device containing said filter element fixed to the housing.
In one embodiment, the downstream filter has a first thread part, and the housing has a second thread part which engages with the first thread part.
In another embodiment, the downstream filter is integrally formed with the housing.
In still another embodiment, the upstream filter is fixed to the downstream filter via fitting.
Preferably, the upstream filter and the downstream filter are in the form of cylinder and so arranged that one nests in the other.
The upstream and downstream filters may have the same or different filter membrane selected from the group consisting of a pleated type, roll type or seamless fiber cylinder type depth filter containing nonwoven fiber mass; and a porous foam, hollow fiber or pleated membrane filter. A roll type filter may comprise various kinds of filter bodies rolled together, and the roll type filter may also have a density gradient.
The upstream filter may be a member selected from a set of filters, which set is different from a set from which a member is selected as a downstream filter.
The present invention also provides a filter device containing the above-mentioned filter element.
The upstream filter comprises, in the order from inside, a porous inner support cylinder made of resin (core), and a filter body in the form of sheet rolled around the core. If necessary, the upstream filter further comprises an outer support cylinder made of resin (sleeve) or alternatively a resin net, which surrounds the filter body. The top edge and the bottom edge of the upstream filter are sealed with resin caps.
On the other hand, the downstream filter comprises, in the order from inside, a porous inner support cylinder (core), a filter body surrounding the core, and a porous outer support cylinder (sleeve) or alternatively a net, which supports the outer surface of the filter body. The top edge and the bottom edge of the downstream filter are sealed with resin caps.
The combination of filters that comprises the filter body can be properly selected depending on the purpose. The upstream filter has a filter body comprising a pleated type, roll type or seamless fiber cylinder type depth filter containing non-woven fiber mass; and a porous foam, hollow fiber or pleated membrane filter. The upstream filter locates upstream the downstream filter in the housing, and it may not be mechanically combined with a downstream cartridge, although it is preferred that both ends of the upstream filter be sealed with caps having the structure which can be mechanically and liquid-tightly combined with the downstream cartridge.
The downstream filter is a filter cartridge having a filter body comprising a pleated type, roll type or seamless fiber cylinder type depth filter containing non-woven fiber mass; and a porous foam, hollow fiber or pleated membrane filter. One end of the downstream filter is sealed with a cap, while the other end is sealed with a cap having a fluid inlet or a fluid outlet. Each of the caps may be combined with the upstream filter via a twist-lock, an O-ring, and/or a thread. However, it may not necessarily be combined.
The materials for the filter body used for the upstream and downstream filters can be selected from those known in the art. Examples include PP (polypropylene), PTFE (polytetrafluoroethylene), UHMWPE (ultra-high molecular weight polyethylene), PE (polyethylene), HDPE (high-density polyethylene), PES (polyether sulfone), nylon, polyester, PVDF (polyvinylidene fluoride), cellulose and SUS (stainless steel). The inside and outside support cylinders of the upstream and downstream filters are made of rigid resin. When a net is used instead of the support cylinder, it can be made of the same material. The top and bottom caps may be in the form of ring or disk, depending on the position at which they are used. They are fused by heat with the top or bottom edge of the laminated structure composed of the inner and outer cylinders (or parts of the net) and the filter body. The material for the caps is also selected from those known in the art.